Patterns of Regeneration between Individual Nerve Cells in the Central Nervous System of the Leech

Abstract

SEVERED axons of nerve cells can regrow towards their original destinations and re-establish synaptic connexions. For example, optic nerve fibres in the frog and goldfish grow back to the appropriate regions of the midbrain^1,2, and motor nerve cells in crayfish reinnervate their original muscles³. The new connexions seem to be correct, in the sense that normal function is restored by regenerating fibres growing back to the region that had been denervated. But it is not known how precisely an individual nerve cell can find its original target. One possibility is that each cell accurately reforms all its original synapses. On the other hand, the mechanism might be less precise, and the result still be functionally adequate or better, even though some cells have become reconnected abnormally. The general question of what happens at the cellular level during regeneration could also be relevant for an understanding of how specific neural connexions are formed during development.